The present invention relates to apparatus for applying an ink image to a receiving material adapted to be moved in an advancing direction, comprising an ink application mechanism for applying an ink image to a strip of receiving material which extends in a direction transverse to the advancing direction of the receiving material and carrier means are provided to keep the strip in a predetermined position with respect to the ink application mechanism, whereby the carrier means comprises a carrier plate for carrying said strip, said carrier plate having channels extending in a direction parallel to the direction of advance of the receiving material.
An apparatus of this kind is known from UK Patent Specification 2 290 753. In the apparatus described therein, the channels in the carrier plate are formed by ribs disposed on the carrier plate. Bubbles formed in the receiving material by the absorption of moisture-containing constituents of the ink and the receiving material can sag by gravity, in the channels which formed in order to avoid contact between the receiving material and an ink application mechanism situated a short distance thereabove and formed by ink heads.
A disadvantage of this known apparatus is that bubbles forming in the receiving material, at places where the receiving material lies on the ribs, can hardly sag in the channels, with the consequent risk that the receiving material may nevertheless still come into contact with the ink heads, thus resulting in undesirable soiling of receiving material and ink heads.
Accordingly, the main object of the present invention is to provide an apparatus which does not contain this disadvantage.
To this end, according to the present invention, the carrier plate is provided with holes and air displacement means are provided which draw air via said holes away from the space between the carrier plate and a strip of receiving material lying on the carrier plate, said holes appearing in the carrier plate at least in a portion thereof in which a strip of the receiving material is maintained in a predetermined position with respect to the ink application mechanism.
As a result, the receiving material is pulled against the carrier plate with a relatively considerable force so that it is possible to ensure, with a great degree of certainty, that parts of the receiving material, particularly bubbles projecting in the direction of the ink application mechanism, remain out of contact with the ink application mechanism. Another effect is that no contact pressure means are required to press the receiving material into the recessed parts of the carrier plate (as known from the European Patent 0 699 537, which also relates to an apparatus according to the preamble), which contact pressure means might obstruct the advance of receiving material and be inoperative at the location of the ink application mechanism.
Preferably, the holes are formed in the ribs forming the channels on the carrier plate and lead into the top surface of each rib. The effect of this is that when the receiving material is used which is not sensitive to the formation of bubbles or other types of deformation, it is pulled flat against the ribs of the carrier plate without parts of the material extending between the ribs being appreciably pulled into the channels and thus, the receiving material remains sufficiently flat during the application of an ink image.
Another effect is that when receiving material is used which is sensitive to deformation, such as bubbles and creases, said material is satisfactorily drawn against the ribs and the negative pressure also forms in the channels between the ribs due to the leakage of air between the holes and receiving material, and said negative pressure pulls the bubbles and creases into the channels in order to keep them away from the ink application mechanism.
Preferably, each channel has a width of between 15 and 20 mm. If the channels have a width less than 12 mm it has been found that the effect is inadequate because the carrier plate then behaves like a practically completely flat plate with bubbles which project in the direction of the ink application mechanism not being drawn into the channels. If the channel width is greater than 20 mm, receiving material which is unaffected by deformation will undergo deformation unnecessarily due to sagging in the wide channels.
If the channels are configured with walls which form an acute angle with the top surface of the carrier plate, then the side edges of a web of receiving material fed over the carrier plate can slide easily over the carrier plate in the transverse direction in the event of skewing and expansion without catching or curling.
If the holes in the carrier plate, as considered in the direction of advance of the receiving material are situated predominantly in an upstream edge portion, then if the said zone is covered solely by a leading part of a web of receiving material, sufficient suction is obtained because leakage air remains substantially absent in the rest of the carrier plate.
According to another aspect of the invention, the holes extend in edge zones of the carrier plate where side edges of receiving material for processing can come into contact with the carrier plate, and, as considered in the direction of advance of the receiving material, over the entire length of the carrier plate. The effect of this is that the side edges of receiving material which are extra sensitive to creasing are kept flat so that ink heads moving in reciprocation in the transverse direction do not collide with these side edges.